What is the biggest mistake that people make when picking stocks?

One of the biggest mistake that people made when investing in stocks is to not do their homework and go into the market due to hearsay.

I made this mistake early in my investing journey and paid the price for that

Buying stocks based on a tip someone gave you, and not doing any due-diligence yourself.

The worst mistake is when people pick stocks like they are picking their nose.

They just want to pick it even when it might turns out ugly.

Joke aside,

Every investment or trade requires a plan and logic needs to there for to supports it.

Logic comes with facts and numbers.

Plans comes with action and reaction.

If a person dun follow facts and dun like numbers, and the action and reaction are usually the sad ones.

Hope this short answer helps.

I think this could be a phenomenon where people just choose to follow the "herd" and where prices look like an upward trend, people just buy. The converse would most probably be true as well. I think the failure here would be not actually understanding what you are buying into.

Another potential troublesome phenomenon would just be letting your emotions take over you and making panic decisions. Like what others have mentioned, I think a lack of understanding and research can be more of an issue here. And if you are merely following the crowd, you tend to miss on certain opportunities also,